Star Wars Celebration shares many similarities with Comic-Con, but is exclusively focused on the galactic franchise first brought to the big screen by George Lucas. The four-day-long conference isn’t a deep dive into a galaxy far, far away – it’s a rocket launch into the minutia of this expansive universe. From a panel celebrating the 40th anniversary of the very first Star Wars movie; to a sneak peek at a trailer for The Last Jediand season four of the animated TV series Star Wars Rebels; plus discussions on how to build your own droid; how to find out-of-print collectables; or start your own podcast, there is no detail left unexamined.

One of the most revealing discussions came on Friday from the team behind Rogue One. All of our most burning questions were answered like: how did they CGI a dead guy back to life and how did they squeeze Alan Tudyk inside of K-2SO’s skinny frame? Executive producer and visual effects supervisor John Knoll guided us through the process of making Rogue One alongside production designer Doug Chiang, supervising sound editor Matthew Wood, and co-producer John Swartz.

They went step by step explaining the intricate process of using motion capture technology and visual effects to secure an appearance by Peter Cushing, who passed away more than twenty years ago. First, stand-in actor Guy Henry played the part on set while wearing motion capture sensors on his face. Later, Cushing’s likeness was copied from a cast of his face made during the filming of the original Star Wars. In the post-production phase, the effects team would constantly compare the resulting image with shots from Cushing’s pre-existing performance as Grand Moff Tarkin from the 1970s.

The biggest laughs came when the team revealed Alan Tudyk improvised many of K-2SO’s funniest moments. During the shoot, Tudyk – often standing on stilts to match the height of the oversized droid – wore a suit covered with sensors to capture his ad-libbed movements. Then, it fell on the special effects crew to create a digital mask of K-2SO to replace Tudyk. Unlike C-3PO and R2-D2, this robot doesn’t have a human actor (literally) inside of him.

In one scene, the sassy K-2SO is forced to pretend his companions Cassian (Diego Luna) and Jyn (Felicity Jones) are prisoners. In order to assert his dominance and convince the Stormtroopers he means business, K-2SO slaps his master in the face. Diego Luna, caught off-guard since the droid-on-human violence didn’t exist in the original script, begins to laugh and uses his hand to cover his face in order to not ruin the shot. Thanks to Luna’s quick thinking the sequence ended up in the final film.

On a gigantic screen, Rogue One‘s production team played unedited clips of Alan Tudyk in a motion capture suit side-by-side with the CGI-enhanced footage of K-2SO’s final look. The attendees couldn’t get enough of Diego Luna’s reaction, cracking up as the clip repeated on a loop.